The present invention relates to automobile body structures and more particularly to a lightweight automobile body structure.
Automobile manufacturers continuously strive to increase vehicle fuel economy and performance through the introduction of advanced engine technology, hybrid electric or fuel cell powered drivelines, more efficient, lightweight drivelines, as well as lightweight body structures. When considering fuel economy, a vehicle""s weight plays a significant role and thus, a vehicle""s body structure is a major focus of weight reduction. However, the body structure plays a significant role in supporting other vehicle components, protecting passengers in cases of impact, and overall vehicle performance. Because of this, the body structure is required to maintain particular strength and impact characteristics for passenger protection, as well as bending and torsional stiffness to maintain vehicle performance.
The body structure is a load carrying mechanical member experiencing a variety of load types including concentrated, distributed, axial and torsional loads. When analyzing the body structure, three points are considered: strength, stiffness and stability. Under an applied load, the body structure""s strength is its ability to resist permanent deformation. Stiffness is its ability to resist deflection and stability is its ability to retain its equilibrium configuration. Each of these points is a function of the particular cross-section, the amount of material forming the body structure, and the mechanical characteristics of the material used.
One approach to designing a lightweight body structure has been the introduction of materials that are lighter than traditional materials while maintaining comparable strength and stiffness characteristics. Some of these materials include composites, carbon fiber, aluminum, magnesium and the like. One significant drawback from using such materials is their cost, being significantly higher than that of steel and other traditional materials. Another drawback is the complex manufacturing required to form the body structure components from such materials. Manufacturing complexity increases the total vehicle cost and therefore, there is a trade off between attaining a reduced weight and increasing the vehicle cost.
Therefore, it is desirable in the industry to provide an improved lightweight automobile body structure, in particular a body frame, that maintains required strength, stiffness, and stability characteristics for meeting passenger safety and vehicle performance standards. Additionally, the body structure should be manufacturable using existing technologies and materials to attain a reduced weight without increased cost. Furthermore, the body structure should enable a total component reduction to further decrease cost and manufacturing time.
Accordingly, the present invention provides a lightweight automobile body structure. The body structure has a base assembly including an upper sheet and a lower sheet. The upper sheet has first and second series of upper reliefs formed therein and the lower sheet has first and second series of lower reliefs formed therein. The upper and lower sheets are stacked adjacent one another, whereby the first series of upper reliefs are in flush contact with the first series of lower reliefs and the second series of upper reliefs are offset from the second series of lower reliefs for defining a space therebetween. The second series of upper and lower reliefs define torque box structures, functioning as thin-walled tubular members having non-circular cross-sections.
The body structure further includes first and second side panels fixedly attached to the base assembly and extending therefrom for defining respective sides and a roof panel fixedly attached between the first and second side panels for defining a roof. In this manner, a unitized automobile body structure is provided with the upper and lower reliefs of the base assembly defining torque box sections and ribs for optimizing structural efficiency.
Further, because of the optimized structural efficiency, the upper and lower sheets of the base assembly are thin, having a thickness of no greater than 4 mm, and preferably 2 mm or less. In this manner, more expensive, lighter weight material may be used and a cost savings still achieved due to the reduced total amount of material required.
Additionally, the components of the base assembly are preferably die cast. Die casting of the components provides significant advantages including improved dimensional consistency and lower fixturing requirements over other forming methods, as well as a reduced component count, as several components may be directly formed into the base assembly.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.